The term 'make watertight' refers to the process of preventing water from entering a structure. This can be done by using a variety of materials and techniques, such as calking, caulking, sealing, and sealup. Calking is a process of filling small gaps with a material such as putty or plaster, while caulking is a process of filling larger gaps with a flexible material such as rubber or silicone. Sealing is a process of applying a waterproof material such as tar or asphalt to a surface, while sealup is a process of using a combination of materials to create a watertight SEAL.